Data Sheet

ADN8831

Rev. A | Page 17 of 20

MOSFET DRIVER AMPLIFIER

The ADN8831 has two separate MOSFET drivers: a switched

output or pulse-width modulated (PWM) amplifier, and a high

gain linear amplifier. Each amplifier has a pair of outputs that drive

the gates of external MOSFETs which, in turn, drive the TEC as

shown in Figure 17. A voltage across the TEC is monitored via

SFB (Pin 23) and LFB (Pin 27). Although both MOSFET drivers

achieve the same result, to provide constant voltage and high

current, their operation is different. The exact equations for the

two outputs are

)

25

.

1

(

40

−

−

=

OUT2

B

LFB

V

V

V

)

25

.

1

(

5

−

+

=

OUT2

LFB

SFB

V

V

V

where:

]

V

0

.

4

[

V

5

.

1

<

=

DD

B

V

V

]

V

0

.

4

[

V

5

.

2

>

=

DD

B

V

V

The voltage at OUT2 (Pin 7) is determined by the compensation

network that receives temperature set voltage and thermistor

equations.

0

2.5

5.0

0

2.5

5.0

–5.0

–2.5

0

2.5

5.0

0

0.25

0.75

1.25

1.75

2.25

2.75

OUT2 (V)

Figure 21. OUT2 Voltage vs. TEC Voltage